The universe may itself be considered a black hole, which from our perspective has potential centers everywhere within. Its centers are isotropic from every homogeneous point to their event horizons where the escape velocity exceeds the velocity of light relative to the observer.

The universe has no center or edge in 3D space. The universe is boundless. The overall expansion of the universe is essentially omni-directional (occurs in all directions from every point). Things only appear to be moving away from us because we are only viewing from one reference point. If you were to observe from another distant galaxy, things (including the Milky Way) would appear to be moving away from that point too.

Not all galaxies have a massive center. There are many elliptical/irregular shaped galaxies that are without massive/easily-to-define centers like our own. Photos one sees in the media are usually spiral galaxies because they are so picturesque.

Stretched space is not expected to snap back. It will continue to expand forever...probably at an accelerating pace.

Yes, the universe is still considered "flat" as far as I know. That means it will expand forever. An open universe will expand forever too. The "big freeze" mentioned does not refer to stopped expansion, but rather "heat death" in which all matter falls apart and all energy is reduced to ground state....the universe is left as a cold, thin soup of fundamental particles with no useful energy.

Although Loren's post makes for an interesting discussion, I think it's confusing Viper's topic. By definition, a black hole is an object residing within spacetime, not the whole of spacetime itself. But the similiarities are worth a separate topic of discussion.

I don't buy Hawkings thought that because some energy radiates OUT that a black hole will eventually "evaporate". More stuff goes in; it becomes more massive; its gravity increases; it eats more stuff.

If black holes continue forming -- and consuming matter/energy -- then doesn't it follow that EVENTUALLY black holes will suck in everything in between, until they all "unite" into a singularity (AGAIN!)?

There's your "Big Crunch"...and a brief look at the "life cycle" of the Universe...an Eternal Entity of Energy that reincarnates from Big Bang to Big Bang.

Originally posted by Viper But then if you look at all of the galaxies they are swirled around a centre or central area or an object(s) of intebse gravity

The unviverse has no centre because it is not expanding from a single point like an explosion but rather every bit of space increases in size and then that it turn increases in size. The galaxies are not centred around a 'central area' (as far as we know).

I don't buy Hawkings thought that because some energy radiates OUT that a black hole will eventually "evaporate". More stuff goes in; it becomes more massive; its gravity increases; it eats more stuff.

As I recollect Hawkings work, the radiation is not from the center of the Black Hole, but from the interaction of the 'event horizon' with the 'fabric' of space/time.

The Black Hole itself radiates nothing! (loses no mass)

A Black Hole does NOT "eat it's neighbourhood" as it is a gravitational well that only increases in size relative to the mass within it, so it is NOT like a vacuum cleaner sucking up everything around it, it simply empties the space around it to a decreed limitation that is imposed by the Modus Operandi of Gravity.

After that, it is up to the mass to get close enough for the gravity to take hold and effect it, suck it in.

yes it will over time. But, eventually you run out of matter, and the black hole will evaporate. This is why it is generally said that stellar sized black hole has a lifetime of about a googol years (the bigger the hole, the much longer it takes).

I should point out to you that all the black holes that form will NOT colesce into one giant one. The universe will be expanding so fast that far in the future, that it'd be lucky if a black hole was within the present diameter of the universe from another black hole. And as was pointed out, black holes merely empty the space surrounding them.

That means if the sun suddenly was replaced by a black hole of equal mass, all objects would continue to orbit the black hole as they presently do...exception being Mecruy due to its proximity, but even then it is doubtful it would be pulled in.

And as was pointed out, black holes merely empty the space surrounding them.

That is quite true for the Short ranging of gravities ability, but , Gravity is presently thought of as having Infinite range, till that is proven differently, we must accept, that given enough time Gravity will win out over everything else, and all will be drawn back together into a, well, whatever is the center of a Black Hole, presently thought of as a singularity.

Well all things equal that is correct. However, there is that rather odd acceleration to the expansion of the universe that pretty much seals the universe's fate as the heat death.

And yes gravity has infinite range...but does that mean the gravity has the same strength? Nope. If matter is traveling sufficiently fast enough (as it would be) and if space is expanding fast enough (as it would be) then the matter will just keep on going until eventually it runs into whatever black hole it may encounter, if any.